Installation comprising two or more free piston engines



arch 14, 1967 J. B. GUY ETAL 3,308,796 2 INSTALLATION COMPRISING TWO OR MORE FREE PISTON ENGINES Filed March 22, 1965 5 Sheets-Sheet 1 ATTORNEYS arch 14, 1967 I INSTALLATION COME-RISING Two OR MORE FREE PISTON ENGINES Filed March 22, 1965 J. B. GUY ETAL C5 Sheets-Sheet 2 ATTORNEY; I

March 14, 1967 Filed March 22, 1965 J. B GUY ETAL INSTALLATION COMPRISING TWO OR MORE FREE PISTON ENGINES Sheets-Sheet 5 ATTORNEYS United States Patent 3,308,796 INSTALLATION COMPRISING TWO OR MORE FREE PISTON ENGINES Jean Baptiste Guy and Auguste Moiroux, Lyon, and Edmond Sale], Meyzieu, France, assignors to Societe dEtudes et de Participations, Eau, Gaz, Electricite, Energie, S.A., Geneva, Switzerland Filed Mar. 22, 1965, Ser. No. 441,452 Claims priority, application France, Apr. 1, 1964, 969,427 11 Claims. (Cl. 123-46) The invention relates to the means for maintaining a determined difference of phase (it should be understood that the expression difference of phase includes also a difference of phase equal to zero, in other words is intended to include the case where the free piston engines operate in coincidence of phase) among several free piston engines comprising a driving part operating, preferably, according a two-strokes diesel cycle and a compressor part for compressing air, these free piston engines being either motocompressors used for the supply of compressed air or autogenerators wherein at least an essential part of the air compressed in their compressor parts is used as feeding and scavenging air for the driving part, the latter supplying, through its exhaust ports, a mixture of scavenging air and of uncompletely expanded combustion gases to a receiver machine for instance to a turbine for the driving thereof.

It is already known to interconnect the pneumatic accumulators of return energy (hereafter referred to under the word *cushions) of said free piston engines, through communication duct means and to provide therein a valve which permits, when the predetermined difference of phase is perturbated, the transfer of certain amounts of air from the cushions of the engine which is leading in phase to the cushions of the engine which is lagging in phase, whereby the leading engine is retarded and the lagging engine is accelerated until the desired predetermined difference of phase is reestablished.

The object of the invention is to improve the means which control the predetermined difference of phase among several free piston engines in particular in connection with the reliability of their use and the simplification of their construction.

According to the invention, the communication means provided between the cushions of two free piston engines are connected in a manner such that they be opened twice during each complete cycle of operation of said engine, namely a first time during a period of time which depends upon the motions of the pistons of one of said engines and a second time during a period of time which depends upon the motions of the pistons of the other of said engines, said two periods of opening being chosen in a manner such that, when the two free piston engines operate with the desired predetermined difference of phase the quantities of air which flow during these periods from the cushions of one of the engines to the cushions of the other engine equal the quantities of air which flow in the opposite direction, whereas in the case where the predetermined difference of phase is perturbated the quantities of air transferred from the cushions of the engine leading in phase to the cushions of the engine lagging in phase are greater than the quantities of air transferred in the opposite direction until the predetermined difference of phase be reestablished.

It should be understood that the expressions complete cycle of operation of a free piston engine or cycle of operation of free piston engine refer to the sum of one outwards stroke and of one inwards stroke of the pistons of said free piston engine.

The invention will be more fully described therein in connection with particular preferred embodiments given ice merely by way of example with reference to the appended drawings in which FIG. 1 shows diagrammatically two free piston engines comprising means according to the invention to maintain a predetermined difference of phase of operation between two autogenerators;

FIG. 2 shows diagrammatically a hydraulic device for controlling a valve provided within a duct connecting the cushions of the autogenerators of FIG. 1;

FIG. 3 shows diagrammatically a mechanical device for controlling a valve provided within a duct connecting the cushions of the autogenerators of FIG. 1;

FIG. 4 is a section along line IV-IV of FIG. 3;

FIG. 5 is a diagram showing the variations of pressure in the cushions of the two autogenerators of FIG. 1 when these autogenerators are to be operated with a predetermined difference of phase of 180, as well as the quantities of air transferred from the cushions of one of the autogenerators to the cushions of the other autogenerator in the case of such a difference of phase;

FIG. 6 shows the variations of the pressure in the cushions of the two autogenerators when the actual difference of phase has deviated from the predetermined and desired difference of phase of 180 and the influence of such deviation upon the quantities of air transferred from the cushions of one of the autogenerators to the cushions of the other autogenerator;

Finally FIG. 7 is a similar diagram showing the application of the invention to the case where the chosen predetermined difference of phase to be maintained between two autogenerators is of instead of Concerning the autogenerators per se, between which a predetermined difference of phase is to be maintained they may, except for the means provided therefor by the invention, be arranged in any appropriate manner, for instance as shown diagrammatically in FIG. 1 which shows two autogenerators A and B each of which comprises a motor cylinder 1, two opposite pistons 2 and 3 working therein according to the two-strokes diesel principle and said pistons 2 and 3 controlling in a known manner inlet ports and exhaust ports (not represented) provided in cylinder 1. The injection of fuel is effected through injector means (also not represented) when the pistons 2 and 3 approach their respective interior dead end centres.

These motor pistons 2 and 3 constitute with compressor pistons, respectively designated at 4 and 5, moving free piston assemblies.

The two piston assemblies of a same autogenerator are interconnected by a synchronisation mechanism comprising a crank 6 oscillating about a fixed axis 7 and articulated, through connecting rods 8 and 9, to rods 10 and 11 which are in turn secured respectively to the compressor pistons 4 and 5, said rods 10' and 11 moving parallely to themselves together with these pistons.

The pistons 4 and 5 reciprocate respectively in the compressor cylinders 12 and 13 and divide said compressor cylinders, respectively, in two compartments, the inner compartments being designated at 12a and 13a and the outer compartments at 12b and 13b.

The compartments 12a and 13a constitute the effective compressor spaces which are filled with air through inlet or suction valves (not represented) during the outwards strokes of the pistons 4 and 5, such air being then compressed and delivered, during the next inwards strokes of the pistons 4 and 5, into a casing forming a reservoir of feeding and scavenging air for the cylinder 1 of each said autogenerators.

The compartments 12b and 13b constitute pneumatic accumulators of return energy containing air cushions which store the greatest part of the energy generated in the motor cylinder 1, during the outwards strokes of pistons 4 and 5, said cushions then restoring the stored energy to the piston assemblies 2, 4 and 3, 5 for their inwards strokes. These inwards strokes permit, on the one hand, the compression of the air sucked in the compressor spaces 12m and 13a during the preceding outwards strokes and, on the other hand, also the compression of the combustion air which is confined within the cylinder 1 between the two motor pistons 2 and 3.

A duct 14 connecting the cushions 12b and 13b provides for the equality of the instantaneous pressures in said cushions. Considering now the means for maintaining a determined difference of phase between the free pistons respectively 2, 4 and 3, 5 of the two autogenerators A and B, they comprise two communication ducts 15 and 16 interconnecting the pneumatic accumulators of energy of the autogenerators A and B, two by two, duct 15 interconnecting namely the two accumulators or cushions 12b and duct 16 interconnecting accumulators or cushions 13b of said autogenerators.

Moreover valve means 17 and 18 are provided in said ducts 15 and 16 respectively for either closing or opening in conditions which will be set forth below.

According to the main feature of the invention these valve means 17 and 18 are controlled in a manner such that, for each complete cycle of operation of the two autogenerators A and B, each of said valve means opens once but at different periods of time predetermined in a manner such that, when the pistons of the two autogenerators A and B operate in their respective motor cylinders with the correct dilference of phase, the quantities of air which are transferred from the accumulators of the autogenerator A to the accumulators of the autogenerator B during said periods of opening of said valve means, equals the quantities of air which are transferred from the accumulators of autogenerator B to the accumulators of autogenerator A, thus in the opposite direction during the same periods of opening of said valve means, whereas the quantities of air transferred from the leading autogenerator to the lagging autogenerator are superior to the quantities of air transferred in the opposite direction when said determined diiference of phase is perturbated, whereby the determined and desired difference of phase can be restored. This may be obtained by controlling the opening of one of said valve means, for instance of valve means 17, in relation with the strokes of the piston assemblies of autogenerator A in a manner such that these valve means open once per cycle of operation of said autogenerator, whereas the opening of valve means 18 is controlled in a similar fashion by the strokes of the pistons of autogenerator B.

Preferably the opening of each of said valve means 17 and 18 is controlled while the pistons of the corresponding autogenerator operate their inwards strokes and, in particular, advantageously during a period of these strokes for which the variations of pressure in the cushions of said autogenerator are the most important.

In order to exclude any influence that a variation of the strokes of the pistons could have on the maintaining or reestablishing of the desired predetermined difference of phase between the autogenerators, the periods of opening of valve means 17 and 18 take place during the part of the strokes of the free pistons which is limited, in one direction, by their interior dead end centre the remotest from the centre of the engine (hereafter designated by PMi max.) and by their exterior dead end centre the closest of the centre of the engine (hereafter designated by PMi min).

The shifting in time between the periods of opening of the two valves 17 and 18 depends upon the predetermined difference of phase which must be maintained between the two autogenerators. When the desired predetermined diiference of phase is equal to 180, valves 17 and 18 are controlled to open and to close in correspondance with respectively the same positions of the respective piston assemblies in the cylinders of the corresponding autogenerators. On the contrary if the desired difference of phase is less than 180, for instance if it equals the beginning and the ending of the periods of opening of each of said valve means in connection with the strokes of the pistons of the corresponding autogenerators must be chosen differently for each of said nutogenerators.

In order to illustrate these features, reference will be made to FIGS. 5 to 7. In these figures a curve a indicated by a continuous line shows diagrammatically the variation of the pressure P in the cushions of the autogenerator A in function of the time T whereas the curve b, indicated by a dotted line, shows diagrammatically the variation of the pressure in the cushions of the autogenerator B in function of the time.

In FIG. 5 curves at and b are shown in the mutual positions corresponding to a desired difference of phase of The period of opening of the valve 17 (period which depends upon the strokes of the pistons of the autogenerator A) is indicated on the abscissa (axis on which the times are recorded) by a small rectangle 17a the contour of which is indicated by continuous lines, whereas the period of opening of the valve 18 is indicated on the same axis by a small rectangle 18b represented in dotted lines.

As shown in FIG. 5, the beginning and the end of the opening period of the valve 17 are shown respectively by the point d and f,,, on the part of the curve a which extends between the exterior dead end centre PMe and the interior dead end centre PMi of the piston assemblies of the autogenerator A.

The time interval between the instant at which the pistons of the autogenerator A are in their exterior dead end centre, shown by the point PMe,,, and the beginning of the period of opening d of valve 17 is shown equal to x,,, whereas the interval of time between said exterior dead end centre point 'PMe and the end f of the period of opening of valve 17 is shown to be equal to y Concerning now the period of opening 18b of valve 18, it is located in an identical relationship with respect to the curve b than the period of opening of valve 17 with respect to the curve a. Consequently the interval of time x between the starting point d of the period of opening 18b and the instant at which the pistons of the autogenerator B are in their exterior dead end centres shown by the point PMe is equal to x and the interval y between the exterior dead end centre point PMe and the ending tirne f of the period of opening of valve 18 equals ya- As shown equally in FIGURE 5 the periods 17a and 1812 are located in a manner such that they extend on either side of the intersections of curves a and b. This choice for determining the period of opening of the valves 17 and 18 with respect to the reciprocation of the pistons is not compulsory, but appears as preferable owing to the fact that the transfer of air is minimum in these conditions.

As it has been set forth thereabove, the lengths of the periods of opening of the valves 17 and 18 are determined in a manner such that, in each complete cycle of operation of the autogenerator A and of the autogenerator B, the quantities of air transferred from the former to the latter be the same than the quantities transferred in the opposite direction.

In FIG. 5, the quantities of air transferred from autogenerator A to autogenerator B during the period 17a corresponds to the surface Q whereas the surface Q represents the quantities transferred in the same direction during the period 18b of opening of the valve 18.

In a similar fashion the surfaces Q and Q show respectively the quantities of air transferred from the autogenerator B to the'autogenerator A during the periods of opening 17a and 18b of valves 17 and 18 per complete cycle of operation of said autogenerators.

It can be seen that sum Q -l-Q is equal to Q +Q and, consequently, that there is a balance between the masses of air transferred between the cushions in the opposite directions during a same cycle of operation, whereby the difference of phase of 180 remains unchanged.

However if autogenerator A starts leading in phase with respect to autogenerator B the curve a will be displaced with respect to the curve b as for instance shown in FIG. 6. The locations of the periods of opening 17a and 18b with respect to their respective curves do not change, to wit the values x y and x y remain the same with respect to the exterior dead end centres of their respective autogenerators.

However the shifting of the curve a carries along therewith a corresponding shifting of the period 17a with respect to the curve b and equally a shifting of the period 18b with respect to the curve a.

These shiftings result in a substantial increase of the quantities Q and Q and in a substantial reduction of the quantities Q and Q Consequently, the sum of the surfaces Q +Q i.e. of the total quantity of air which is transferred from autogenerator A to autogenerator B during a complete cycle becomes far superior to the sum of the surfaces Q +Q corresponding to the total quantity of air which is transferred from autogenerator B to autogenerator A.

As a result autogenerator B is accelerated whereas autogenerator A is retarded until both autogenerators are again working with the desired difference of phase of 18 FIG. 7 shows the positions of curves a and b and the locations of the periods of opening 17a and 18b of valves 17 and 18 in the case where the desired difference of phase to be maintained, and if the case should be to be set back, between the two autogenerators, is of 120.

In this case, the periods of opening 17a and 18b are also operated during the return strokes of the pistons in their respective autogenerators.

However the position of the period 17a with respect to curve a is not the same anymore than the position of the period 18b with respect to curve b for obtaining, with in a complete cycle of operation of said autogenerators, an equality of the quantities of air transferred during these periods of opening, on the one hand, from autogenerator A to autogenerator B and, on the other hand, from the autogenerator B to the autogenerator A.

In order to provide for this equality (equality of the surfaces Q and Q, in FIG. 7) the time intervals x and y between the exterior dead end centre PMe of the piston of the autogenerator A and, respectively, the beginning and the end of the period of opening 17a must be greater than the analogous time intervals x y which separate the beginning and the end, respectively, of the opening period 18b from the exterior dead end centre point PMe; of the pistons of autogenerator B.

If these curves are shifted with respect to each other, namely when the difference of phase between the two autogenerators isshifted with respect to the desired 120 value, there is obtained, in a manner similar to the preceding case, an increase of the quantity of air transferred from the leading autogenerator to the lagging autogenerator and a reduction of the quantity of air transferred in the opposite direction, whereby the lagging autogenerator is accelerated and the leading one is retarded until the desired 120 difference of phase is reestablished.

Many embodiments can be devised for causing the opening of valves 17 and 18 during the periods 17a and 18b. According to one of the preferred embodiments, the opening of the valve 17 during the periods set forth above is caused by means operative by the pistons of autogenerator A and the opening of valve 18 is caused by means operative by the pistons of autogenerator B. These means which may be of a mechanical, hydraulic, electrical, of difierent nature must be devised in a man ner such that they cause the opening of the corresponding valve only once per complete cycle of operation of the pistons of each autogenerator.

FIGURE 1 shows diagrammatically hydraulic means, operative by the piston of autogenerator A, for controlling the valve 17 and mechanical means operative by the piston of autogenerator B for controlling the valve 18.

Of course, it will be practically more convenient to control the valves 17 and 18 through means of a similar nature.

The purpose of showing means of a different nature for controlling valve 17 and 18 is only to limit the number of drawings in the present application.

Advantageously the controlling means of valves 17 and 18 are operated by the oscillating axis 7 of the crank 6 in the synchronisation mechanism 6, 7, 8, 9, of the free piston of each of the autogenerators. For instance a cam 19 is keyed on the axis 7 for operating the hydraulic control means of the valve 17, such means being described here below with reference in particular to FIG. 2.

The above mentioned cam 19 operates the stroke in one direction of a piston 20 against a return spring 21 which ensures the return stroke of the same piston. This piston 20 is slidable in a cylinder 22 the interior of which communicates, through a pipe 23, with a cylinder 24 in which operates a piston 25 integral with the rod of the valve 17. The spring 26 urges the valve 17 in its direction of closing.

A groove 27 is provided in the inner wall of cylinder 22 (see FIG. 2), and a feed duct 28 opens into said groove 27 to permit the communication of the interior space of the cylinder 22 with a source of liquid which can be compressed and delivered by the piston 20 from the cylinder 22 into the cylinder 24 for causing the opening of valve 17 against the spring 26.

Moreover piston 20 is provided with a groove 29 which is connected through a channel 30, equally provided in the piston 20, with the working chamber 31 of the pump formed by the piston 20 and the cylinder 22..

The dispositions of the grooves 27 and 29 in the inner wall of cylinder 22 and piston 20 respectively, the keying or fixing of the cam 19 on the axis 7 and the form of the cam are chosen in a manner such that, when the pistons of the autogenerator A are operating their inwards strokes, the piston 20 separates said groove 27 from the chamber 31 by its edge 20a, at the time indicated by d in the FIGS. 5 and 6. Thus from this time on, the liquid is delivered by the piston 20 into the cylinder 24 and opens the valve 17.

When the piston 20 proceeds further in its cylinder under the action of cam 19, it opens the communication between the working chamber 31 and the groove 27, through the channel 30 and the groove 29, at the time the edge 29a of the groove 29 reaches the level of the edge 27b of the groove 27. At this moment which coincides with the point f of FIGS. 5 and 6, the valve 17 is closed under the action of the spring 26. Thus the opening of valve 17, during the period above mentioned beginning at the point a and ending at the point f of FIGS. 5 and 6, occurs during the upwards progression of piston 20 in cylinder 22, the return stroke of piston 20, which coincides with the outwards strokes of the pistons 2 and 3 of the autogenerator A, having no effect upon valve 17 since the piston 20 sucks liquid during this last movement and thus even cooperates with the spring 26 to hold valve 17 on its seat.

Concerning the mechanical means which may be used for controlling the valve 18 they can be advantageously contrived as indicated in FIGS. 3 and 4. As it can be seen in these figures the control of valve 18 is also operated by means of a cam 32 which, according to FIGURE 1, is fixed or keyed on the axis 7 of the synchronisation mechanism of the autogenerator B.

This cam acts upon the rod 35 of valve 18 through a tappet rod 33 and a double armed lever 34. The valve rod 35 is provided at its upper extremity (FIG. 3) with a plate 36 upon which rests a small roller 37 carried by an extremity of the lever 34 which is pivotable about an axis 38. The valve 18 is maintained on its seat by a spring 39, the upper extremity of which is applied against the under face of the plate 36 and the lower extremity of which is applied against a plate 40 which is normally urged by said spring 33 against a fixed part, for instance a part of the wall of duct 16. The plate 40 which is interposed between the spring 39 and the duct 16 is connected, for instance, through a rod 41 with another plate 42 which is applied above and against the roller 37. The rod 35 of valve 18 passes freely through a hole perforated in the plate 40; in addition said plate 40 carries advantageously above said hole at tube 40a the purpose of which is to guide the rod 35 and the spring 39. The cam 32 which is adapted to control the opening of valve 18 cooperates with a roller 43 mounted at the lower extremity of the tappet rod 33. This cam is provided with an interior groove 32a between a core 32b and two external walls 320 and 32d, these external walls being separated by a passage way 32a. The to-and-fro reciprocations of the piston 2, 4 and 3, 5 of the autogenerator B entails oscillating motions to said cam between the position indicated at PMe, corresponding to the exterior dead end centre of said pistons, and a position indicated in FIG. 3 by PMi, corresponding to the interior dead end centre of said pistons.

When the cam is in the position indicated in FIG. 3, the roller 43 is applied by the plate 42 again-st the interior surface of the wall 320.

When cam 32 start pivoting, the roller 43 remains applied during the starting period of this motion against the interior surface of the wall 320 until the moment it enters in contact with the exterior face of the wall 32d after having passed through the passage way 32e.

The face 32d has a shape such that at the moment indicated by d in FIGS. 5 and 6 it exerts on the roller 43, an outwards push directed radially with respect to the rotation axis of said cam and raises the tappet rod 33 thereby causing the opening of the valve 18 simultaneously with the compression of the spring 39.

The exterior surface 32:; then maintains said valve 18 in its open position by its action on the roller 43 up to the moment the roller 43 passes beyond the back extremity 32 of said wall 32d. At this time the spring 39 closes the valve 18 and at the same time brings the roller 43 in a position facing the entry into the groove 32a.

Consequently, when the pivoting motion of the cam changes its direction (concomitantly with the change in direction of the strokes of the piston assemblies of the autogenerator B), the roller 43 enters the groove 32a. This groove, which is formed between the exterior surface of the core 32b and the interior surface of the wall 32a nears progressively the rotation axis of the cam thereby raising the roller 37 together with the plates 42 and 40 and compressing the spring 39. The latter construction has the effect of urging the valve 18 even more firmly against its seat instead of causing its opening. The roller 43 leaves the groove 32a before the end of the pivoting motion of the cam in the last mentioned direction and is applied again against the interior surface of the wall 32c under the action of the spring 39 which expands and moves the plates 40 and 42 and the roller 37 downwardly but still maintains the valve 18 in its closed position.

The cam 32 is thus again ready to cause the opening of valve 18 during the next inwards stroke of the piston of the autogenerator B.

The means devised according to the invention regardless of their embodiments, for maintaining a predetermined ditference of phase between several free piston engines show numerous advantages with respect to the means already known for achieving the same purpose.

Among these advantages one may cite the following:

(l) The section for the transfer of air is always important and is dependent neither upon the desired pre determined difference of phase not upon the degree of perturbation of said difference of phase;

(2) Owing to the fact that the valves which control the communication between the cushions of the autogenerators are always actuated, whether or not said diiferenceiof phase is 'perturbated, there is no danger that these valves will jam in position at the very moment where such a perturbation occurs;

(3) The valves which control the communication between the cushions of the autogenerator are controlled positively whereby the security of the operation is reinforced;

(4) The'control of the communication between the cushions of the different free piston engines is dependant exclusively upon the positions of the piston assemblies of said free piston engines between which the predetermined diiference of phase is to be maintained;

(5) In the preferred embodiments of the invention the communication between the cushions is operated when the variations of pressure in said cushions in function of the time are very important (corresponding to the parts of the curves a and b which have important slopes) whereby the accuracy in the response of the means for maintaining or reesta'blishing the predetermined difference of phase is increased.

While the invention has been described in connection with particularly preferred embodiments it will be understood that the invention is not limited to these embodiments but is intended to encompass all alternatives, modifications and equivalents as may be properly included within the spirit and scope of the invention as defined by the appended claims, for instance such alternatives wherein the cushions of the two free piston engines are connected through a single duct comprising, either one single valve operated alternatively by the free pistons of either one of said engines, or two valves analogous to the valves 17 and 18 above described and provided in two parallel branches of said connecting duct.

What I claim is:

1. An installation comprising in combination a first and a second free piston engines, each of said free piston engines comprising a motor cylinder, a motor piston reciprocating in said motor cylinder, a compressor cylinder, a compressor piston, rigid with said motor piston and forming therewith a piston assembly, reciprocating in said compressor cylinder, a pneumatic accumulator comprising an air cushion for storing energy during the outwards stroke of said piston assembly and restoring energy to said piston assembly for the inwards stroke thereof,

means for controlling the difference of phase between said two free piston engines at a predetermined value comprising communication means connecting the cushions of said first and second free piston engines, valve means in said communications means, actuator means operative, on the one hand, by the piston assembly of the first free piston engine for opening said valve means once per cycle of operation of said first free piston engine and, on the other hand, by the piston assembly of said second free piston engine for opening said valve means once per cycle of operation of said second free piston engine, said actuator means being adapted to permit the opening of said valve means for periods of time the lengths and positions of which are fixed in relation to said predetermined value of the difference of phase between the said two free piston engines to enable the quantities of air transferred from the cushion of one of the free piston engines to the cushion of the other free piston engine to equal the quantities of air transferred in the opposite direction, during each cycle of operation of said free piston engines, when the latter operate with the predetermined difference of phase.

2. An installation comprising in combination a first and a second free piston engines, each of said free piston engines comprising a motor cylinder, a motor piston reciprocating in said motor cylinder, a compressor cylinder, a compressor piston, rigid with said motor piston and forming therewith a piston assembly, reciprocating in said compressor cylinder, said compressor piston dividing said compressor cylinder in two compartments, the one of said compartments which decreases in volume while said compressor piston operates its outwards stroke defining a cushion of air acting as a pneumatic accumulator of re turn energy for the inwards stroke of said compressor piston,

means for controlling the difference of phase between said two free piston engines at a predetermined value comprising communication means connecting the cushions of said first and second free piston engines, valve means in said communications means, actuators means operative, on the one hand, by the piston assembly of the first free piston engine for opening said valve means once per cycle of operation of said first free piston engine and, on the other hand, by the piston assembly of said second free piston engine for opening said valve means once per cycle of operation of said second free piston engine, said actuator means being adapted to permit the opening of said valve means for periods of time the lengths and positions of which are fixed in relation to said predetermined value of the difference of phase between the said two free piston engines to enable the quantities of air transferred from the cushion of one of the free piston engines to the cushion of the other free piston engine to equal the quantities of air transferred in the opposite direction, during each cycle of operation of said free piston engines, when the latter operate with the predetermined difference of phase. 3. An installation according to claim 2, wherein said first and second actuator means are respectively operated,

by said first and second piston assemblies, to open saidfirst and second valve means during the parts of the strokes of said piston assemblies for which the variations of pressure in the cushions are the most import-ant.

4. An installation according to claim 2, wherein said first and second actuator means are respectively operated by said first and second piston assemblies for opening said first and second valve means during, respectively, the inwards strokes of said piston assemblies.

5. An installation according to claim 2, wherein said first and second actuator means are respectively operated, by said first and second piston assemblies, to open said first and second valve means when said piston assemblies are, respectively, between their interior dead end centre the remotest from the centre of said motor cylinder and their exterior dead end centre the closest to the centre of said cylinder.

6. An installation comprising, in combination, a first and a second free piston engines, each of said free piston engines comprising a motor cylinder, two opposite motor pistons reciprocating therein, two compressor cylinders, two opposite compressor pistons rigid with said motor pistons and forming therewith piston assemblies, reciprocating in said compressor cylinders, respectively, pneumatic accumulators comprising a first and a second air cushions for storing energy during the outwards strokes of said first and second piston assemblies respectively for the inwards stroke thereof, duct means interconnecting the cushions of said two compressor cylinders, a synchronisation device for synchronising the strokes of the piston assemblies of each of said free piston engines comprising a member oscillating about a fixed axis operative by said piston assemblies;

means for controlling the difference of phase between said two free piston engines at a predetermined value comprising communication means for respectively connecting the cushions of said first and second free piston engines two by two, valve means in said communication means, actuator means operative, on the one hand, by the oscillating member of said first free piston engine for opening said valve means once per cycle of operation of said first free piston engine and, on the other hand, by the oscillating member of said second free piston engine for opening said valve means once per cycle of operation of said second free piston engine, said actuator means being adapted to permit the opening of said valve means for periods of time the lengths and the positions of which are fixed in relation of the predetermined value of said difference of phase between said two free piston engines to enable the quantities of air transferred from the cushions of one of the free piston engine to equal the quantities of air transferred in the opposite direction during each cycle of operation of said free piston engines, when the latter operate with the predetermined difference of phase, means cooperating with said actuator means for removing the action thereof on their respective valve means during, respectively, the intervals of time separating the periods of open ing of said valve means.

7. An installation comprising, in combination, a first and a second free piston engines, each of said free piston engines comprising a motor cylinder, two opposite motor pistons reciprocating therein, two compressor cylinders, two opposite compressor pistons rigid with said motor pistons and forming therewith piston assemblies, reciprocating in said compressor cylinders, respectively, each of said compressor pistons dividing its corresponding compressor cylinder in two compartments, the one of said compartments, which decreases in volume while said compressor piston operates its outwards stroke, defining a cushion of air acting as a pneumatic accumulator of return energy for the inwards stroke of said compressor piston, duct means interconnecting the cushions of said two compressor cylinders;

a synchronisation device for synchronising the strokes of the piston assemblies of each of said free piston engines comprising a member oscillating about a fixed axis operative by said piston assemblies;

means for controlling the difference of phase between said two free piston engines at a predetermined value comprising first and second communication means connecting the cushions of said first and second free piston engines, two by two, first and second valve means in said first and second communication means respectively, first actuator means operated by the oscillating member of said first free piston engine for opening said first valve means, once per cycle of operation of said first free piston engine, second actuator means operated by the oscillating member of said second free piston engine for opening said second valve means, once per cycle of operation of said second free piston engine, said first and second actuator means being adapted to permit the opening of said first and second valve means for periods of time the lengths and the positions of which are fixed in relation to the predetermined value of said difference of phase between said two free piston engines to enable the quantities of air transferred from the cushions of one of the free piston engines to the cushions of the other free piston engine to equal the quantities of air transferred in the opposite direction, during each cycle of operation of said free piston engines, when the latter operate with the predetermined difference of phase, means cooperating with said first and second actuator means for removing the action thereof on their respective valve means during, respectively, the intervals of time separating the periods of opening of said valve means.

8. An installation comprising, in combination, a first and a second free piston engines, each of said free piston engines comprising a motor cylinder, two opposite motor pistons reciprocating therein, two compressor cylinders, two opposite compressor pistons rigid with said motor pistons and forming therewith piston assemblies, reciprocating in said compressor cylinders, respectively, each of said compressor pistons dividing its corresponding compressor cylinder in two compartments, the one of said compartments, which decreases in volume while said compressor piston operates its outwards stroke, defining a cushion of air acting as a pneumatic accumulator of return energy for the inwards stroke of said compressor piston, duct means interconnecting the cushions of said two compressor cylinders,

a synchronisation device for synchronising the strokes of the piston assemblies of each of said free piston engines comprising a member oscillating about a fixed axis operative by said piston assemblies;

means for controlling the difference of phase between said two free piston engines at a predetermined value comprising first and second communication means connecting the cushions of said first and second free piston engines two by two, first and second valve means in said first and second communication means respectively, a first piston-cylinder system operative by the oscillating member of said first free piston engine for opening said first valve means, once per cycle of operation of said first free piston engine, a second piston-cylinder system operative by the oscillating member of said second tree piston engine for opening said second valve means, once per cycle of operation of said second free piston engine, the piston of each of said systems defining a working chamber in its corresponding cylinder, an annular groove in the wall of said chamber and a duct for the feeding of said chamber with a liquid opening in said annular groove, another annular groove provided in said piston, duct means connecting the last mentioned annular groove with said working chamber whereby each of said piston-cylinder systems cause the opening of the corresponding valve means upon the reduction of volume of its working chambers and after closure of the annular groove in the wall of said chamber by said piston, the action of said piston cylinder system on said valve means being removed when the annular groove of said piston starts communicating with the annular groove in the wall of said working chamber.

9. An installation comprising, in combination, a first and a second free piston engines, each of said free piston engines comprising a motor cylinder, two opposite motor pistons reciprocating therein, two compressor cylinders, two opposite compressor pistons rigid with said motor pistons and forming therewith piston assemblies, reciprocating in said compressor cylinders, respectively, each of said compressor pistons dividing its corresponding compressor cylinder in two compartments, the one of said compartments, which decreases in volume while said compressor piston operates its outwards stroke, defining a cushion of air acting as a pneumatic accumulator of return energy for the inwards stroke of said compressor piston, duct means interconnecting the cushions of said two compressor cylinders,

a synchronisation device for synchronising the strokes of the piston assemblies of each of said free piston engines comprising a member oscillating about a fixed axis operative by said piston assemblies;

means for controlling the difference of phase between said two free piston engines at a predetermined value comprising first and second communication means connecting the cushions of said first and second free piston engines, two by two, first and second valve means in said first and second communication means in said first and second communication means respectively, a first cam operative by the oscillating member of said first free piston engine, a second cam operative by the oscillating member of said second free piston engine, a first spring and linkage system operative by said first cam for opening said first valve means, once per cycle of operation of the first free piston engine and a second spring and linkage system operative by said second cam for opening said second valve means once per cycle of operation of the second free piston engine, each of said spring and linkage systems comprising a roller coacting with the cam of the corresponding free piston engine, said cam comprising exterior wall portions and an interior groove respectively shaped for, upon oscillation of the cam in one direction, permitting the roller to be driven around said exterior wall portions whereby said spring and linkage system operates the openingof the corresponding valve means and, upon oscillation of said cam in the opposite direction, permitting said roller to enter said interior groove whereby said valve means is urged even more firmly in its closed position.

10. In an installation comprising in combination a first and a second free piston engines, each of said free piston engines comprising a motor cylinder, a motor piston reciprocating in said motor cylinder, a compressor cylinder, a compressor piston, rigid with said motor piston and forming therewith a piston assembly, reciprocating in said compressor cylinder, a pneumatic accumulator comprising an air cushion for storing energy during the outwards stroke of said piston assembly and restoring energy to said piston assembly for the inwards stroke thereof, the process for controlling the diiference of phase between said two free piston engines at a predetermined value which comprises positively interconnecting the cushions of said first and second free piston engines, once per cycle of operation of said first free piston engine and in response to the motions of the free piston assembly thereof and once per cycle of operation of said second free piston engine and in response to the motions of the free piston assembly thereof, determining the beginning of said interconnection and controlling the period during which said interconnection is maintained in relation to said predetermined value and in a mannersuch that, on the one hand, the quantities of air transferred from the cushion of one of said free piston engines to the cushion of the other of said free piston engines be equal to the quantities of air transferred in the opposite direction in each cycle of operation of said engines when the difference of phase between the latter assumes the predetermined value and, on the other hand, the quantities of air transferred from the leading engine to the lagging engine be superior to the quantities of air transferred in the opposite direction when said difference of phase stops assuming said predetermined value until said value is reestablished.

11. A process according to claim 10 wherein the periods during which said cushions are interconnected are chosen so as to encompass the moments where the instantaneous pressures are the same in the cushions of both first and second free piston engines when the difference of phase between the latter assumes the predetermined value.

No references cited.

MARK NEWMAN, Primary Examiner.

W. E. BURNS, Assistant Examiner. 

1. AN INSTALLATION COMPRISING IN COMBINATION A FIRST AND A SECOND FREE PISTON ENGINES, EACH OF SAID FREE PISTON ENGINES COMPRISING A MOTOR CYLINDER, A MOTOR PISTON RECIPROCATING IN SAID MOTOR CYLINDER, A COMPRESSOR CYLINDER, A COMPRESSOR PISTON, RIGID WITH SAID MOTOR PISTON AND FORMING THEREWITH A PISTON ASSEMBLY, RECIPROCATING IN SAID COMPRESSOR CYLINDER, A PNEUMATIC ACCUMULATOR COMPRISING AN AIR CUSHION FOR STORING ENERGY DURING THE OUTWARDS STROKE OF SAID PISTON ASSEMBLY AND RESTORING ENERGY TO SAID PISTON ASSEMBLY FOR THE INWARDS STROKE THEREOF, MEANS FOR CONTROLLING THE DIFFERENCE OF PHASE BETWEEN SAID TWO FREE PISTON ENGINES AT A PREDETERMINED VALUE COMPRISING COMMUNICATION MEANS CONNECTING THE CUSHIONS OF SAID FIRST AND SECOND FREE PISTON ENGINES, VALVE MEANS IN SAID COMMUNICATIONS MEANS, ACTUATOR MEANS OPERATIVE, ON THE ONE HAND, BY THE PISTON ASSEMBLY OF THE FIRST FREE PISTON ENGINE FOR OPENING SAID VALVE MEANS ONCE PER CYCLE OF OPERATION OF SAID FIRST FREE PISTON ENGINE AND, ON THE OTHER HAND, BY THE PISTON ASSEMBLY OF SAID SECOND FREE PISTON ENGINE FOR OPENING SAID VALVE MEANS ONCE PER CYCLE OF OPERATION OF SAID SECOND FREE PISTON ENGINE, SAID ACTUATOR MEANS BEING ADAPTED TO PERMIT THE OPENING OF SAID VALVE MEANS FOR PERIODS OF TIME THE LENGTHS AND POSITIONS OF WHICH ARE FIXED IN RELATION TO SAID PREDETERMINED VALUE OF THE DIFFERENCE OF PHASE BETWEEN THE SAID TWO FREE PISTON ENGINES TO ENABLE THE QUANTITIES OF AIR TRANSFERRED FROM THE CUSHION OF ONE OF THE FREE PISTON ENGINES TO THE CUSHION OF THE OTHER FREE PISTON ENGINE TO EQUAL THE QUANTITIES OF AIR TRANSFERRED IN THE OPPOSITE DIRECTION, DURING EACH CYCLE OF OPERATION OF SAID FREE PISTON ENGINES, WHEN THE LATTER OPERATE WITH THE PREDETERMINED DIFFERENCE OF PHASE. 